92 



RESEARCHES ON FUNGI 



due to light refracted 

 through the subsporangial 

 swelling and focussed on 

 the mass of red proto- 

 plasm heaped up in the 

 stipe just where the stipe 

 joins the swelling (Fig. 

 46, p). The discovery 

 that the subsporangial 

 swelling acts as a lens and 

 that, when the fruit-body 

 is in heliotropic equili- 

 brium, it focusses its light 

 on the mass of red proto- 

 plasm at its base formed 

 the basis of all my 

 further studies on the 

 heliotropism of Pilobolus. 

 The lens action of the 

 subsporangial swelUng 

 was further investigated 

 by means of construction 

 diagrams which, as a 

 result of precise mathe- 

 matical calculations, show 

 how the swelHng refracts 

 light (1) when its axis is 

 parallel to the direction 

 of the incident rays of 



Fig. 47. — A median longitudinal section through the upper part of a fruit-body of 

 Pilobolus Kleinii, just before the discharge of the projectile. The gun is shown 

 directed not toward the sourc§ of light but at an angle of 19° thereto, in which 

 position it is not, heliotropically (or photochemically), in a condition of 

 physiological equilibrium. 



The section is exactly the same as that shown in Fig. 46 and there fully 

 described. Again we have : the sporangium filled with spores and covered 

 by an outer black cell-wall o, now broken and allowing an inner basally-situated 

 thick gelatinous ring i to bulge outwards ; the subsporangial swelling, 

 capped by the columella c and passing below into the stipe, its thin cell-wall 

 covered by a layer of protoplasm which is everywhere thin except at r where 



